Our summer group writing project reviewing the integration of X-ray photoelectron spectroscopy (XPS) with oxide thin film synthesis is out in the Journal of Materials Research! This invited review for the Early Career Scholars issue focuses on ways to improve film growth using XPS, accurately interpret XPS data, and design experiments to probe charge transfer and band alignment at interfaces. We use this framework to review many of the current research areas focusing on interfaces in complex oxide heterostructures. One of the recurring themes is the importance of in situ studies to decouple the effects of interfacial phenomena from the effects of atmospheric exposure. We hope that an audience of film growers and spectroscopists will appreciate our perspective!